The present invention relates to a tap holder for holding a tap for tapping and for equipping with a machine tool spindle.
When tapping is carried out by a machine tool by utilizing synchronization with feeding and rotation of a machine tool spindle, rotation and feeding of the machine tool spindle are controlled to synchronize in accordance with a pitch of a tap. However, in actual tapping, owing to a phenomenon referred to as servo delay, an amount of running a tap while machining by rotating becomes larger, or conversely smaller than a tap pitch per rotating the machine tool spindle, tapping is progressed fast or slow by an incoincidence of spindle feeding and rotation, and therefore, a deviation is brought about among an amount of spindle feeding per rotation and a tap pitch. Although in a background art, the incoincidence is prevented by providing floats on both sides in an axial direction of a tap holder, in recent years, the floats are eliminated and the tap holder are an integral structure is constituted by a promotion in an accuracy of synchronizing (synchronizing) spindle rotation and feeding by a development of a mechanism or a control technology.
Further, a tap holder deals therewith by being separated into a tapper body and a tap collet to allow a size of a tap by the tap collet. Also a synchronized tap holder constituting an object of complete synchronization is separated into a tapper body and a tap collet and when the tapper body and the tap collet are connected, the tap collet is attached thereto as gapless as possible.
However, although a synchronization accuracy of the machine tool is promoted, for example, when a spindle feeding direction and a spindle rotating direction are switched in order to draw a tap from a subject work, rotation of a machine tool spindle does not synchronize with spindle feeding and a small sift of the tap in an axial direction cannot completely be excluded from being brought about, and therefore, there is a drawback of enlarging or leaning a screw thread.
As a constitution of absorbing such a synchronization error, there is proposed a constitution in which a tap mounting portion is made to be movable (able to sift) in a rotating axis direction of a spindle by connecting a spindle mounting portion and the tap mounting portion by way of a leaf spring (refer to Patent Reference 1, paragraph No. [0011] shown below), or a constitution in which as in a background art, a tension spring and a compression spring are urged in directions reverse to each other in an axial direction between a spindle and a tap collet and the tap collet is stopped at a position for balancing urge forces, when an error of feeding the spindle is brought about in tapping and a feed amount and a pitch of a tap are incoincident, the spindle is slid slightly in a direction of making the feed amount and the pitch coincident by reacting with an external force from the tap at a front end thereof (refer to Patent Reference 2, paragraph number [0030], FIG. 2 shown below), or a constitution in which a tap driver is provided with a spiral coil having a compressing performance and an extending performance, an attachment body is moved by a small amount in an axis line direction in accordance with a predetermined force exerted to a tap to be able to synchronize (refer to Patent Reference 3, paragraph number [0018], FIG. 2).
However, the constitutions described in Patent References 1 through 3 pose a problem that structures are complicated in any of the cases and cost becomes expensive.
Further, although Patent Reference 4 shown below describes a tap holding apparatus in which in order to lock a tap to a tap holding shaft, a lock bolt is used, at a position opposed to the lock bolt, an elastically deformable bush is filled between a fixing pin brought into contact with an outer peripheral face of a handle portion and an inner wall of a long hole provided at the tap holding shaft, the fixing pin and a lock ring is made to be pivotable in a circumferential direction relative to the tap holding shaft, and the bush is filled also at a gap between the fixing pin in an axial direction and the inner wall of the long hole (page 8, line 14 through page 9, line 10), such a tap holding apparatus prevents the lock bolt from being loosened by restraining a rotational force and a force in a direction of pressing the tap from being operated to the lock bolt and is not for restraining a synchronization error of spindle feeding and rotation of a spindle.
That is, the fixing pin arranged with the bush is brought into contact with an outer peripheral face of the tap operated with a force in an axial direction to lock when the synchronization error of feeding and rotation of the spindle of the machine tool is brought about, and therefore, the force in the axial direction operated to the tap is not sufficiently transmitted to the fixing pin, and even when the elastically deformable bush is arranged on a front side in the direction of pressing the fixing pin, a difference between an amount of moving the top holding shaft and an amount of spontaneously running the tap cannot be absorbed.
Further, Patent Reference 5 shown below discloses a tapper mechanism in which a first member and a second member are connected by a connecting pin and an elastic member in a ring-like shape, further, a clutch for reverse rotation and a connecting member (key member) are connected by the connecting pin and the elastic member (refer to paragraph numbers [0009], [0018] FIGS. 3, 7). However, even the elastic member arranged at either of the connecting pins is for alleviating an impact when a clutch for regular rotation is engaged, or for absorbing attachment error of the connecting member and the clutch for reverse rotation, and not for restraining a synchronization error between spindle feeding and rotation of the spindle.    Patent Reference 1: JP-A-7-60544    Patent Reference 2: JP-A-2004-142033    Patent Reference 3: JP-A-2002-46020    Patent Reference 4: JP-UM-A-59-8725    Patent Reference 5: JP-A-2000-61729